Disrupted sleep may accelerate cancer growth

Fragmented sleep marked by frequent awakenings can speed up cancer growth, increase tumour aggressiveness and weaken the immune system's ability to control or eradicate early cancers. According to researchers from the University of Chicago, fragmented sleep changes how the immune system deals with cancer in ways that make the disease more aggressive. The researchers also investigated the effect of sleep apnoea in children.

Duration: 18min 53sec

Broadcast:
Mon 19 May 2014, 5:40pm

Guests

Transcript

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Norman Swan: We often talk about risk factors for cancer on the program; smoking, obesity, alcohol, some viruses, toxins and family history, for instance. But that list fails to explain completely why most people develop a tumour. So the hunt is on for other things.

Some researchers reckon that sleep is a factor, and worryingly for those of us who wake up a bit during the night, particularly fragmented sleep.

It's the interest of David Gozal who's Professor of Paediatrics at the University of Chicago. He's made some fascinating discoveries.

David Gozal: Several lines of evidence have come over the years, particularly from the epidemiological field. The first studies looked at potential risk factors that would adversely affect mortality. And of course the cardiovascular system came as the first one. The second one came as cancer. And both of them were linked to sleep duration. If you slept too little or if you slept too much, you appear to have an incremental risk of dying of either cardiovascular disease or of cancer.

Norman Swan: Too little or too much is not good.

David Gozal: That's correct. These studies were repeated several times, but they've always relied on the simple question; how long do you sleep? And it's a question that is quite unreliable, to be frank. They did not tackle sleep quality, they don't tackle anything else, and this is where the field was until about two years ago where a model of sleep apnoea with episodic levels of low oxygen levels in the blood, they showed in rats who had the melanoma that they seemed to have larger tumours.

So two groups took a look at two cohorts, they were longitudinal cohorts. One, a study that was done at the University of Wisconsin in Madison by Javier Nieto. Javier found that in their cohort that they had been following for sleep apnoea for many years, almost 20-some years…

Norman Swan: This is not a rat cohort, this is a human cohort.

David Gozal: This is a human cohort, absolutely. They found that if you had sleep apnoea and you had cancer, you had a higher risk of complications of cancer and poorer outcomes.

Norman Swan: And what about cancer incidence?

David Gozal: The cancer incidence appeared to be also increased.

Norman Swan: This is across all tumours?

David Gozal: Across all solid tumours, that's the only thing that they could verify.

David Gozal: That's correct, prostate cancer, breast cancer and so on. So this was an initial observation that of course needed to be verified. Then the Spanish group, also a longitudinal cohort, but they were able to look at it a little bit differently. They looked at a group of cancer patients with sleep apnoea and a group of cancer patients without sleep apnoea. They found that those with sleep apnoea had a much worse outcome, they were more likely to die or they were more likely to have a lack of response to therapy.

Norman Swan: And how sure were they that it was the sleep apnoea? Because if you've got sleep apnoea you're more likely to be fat, you're more likely to have heart disease, you're more likely to have high blood pressure. They could be doing it, not the sleep apnoea.

David Gozal: Absolutely, and statistics adjust for all these confounders, their populations were matched to look at the obesity and so on, but nevertheless you can always raise that question, although it seemed that in both studies, it seemed that it correlated with the measures of severity of sleep apnoea.

Norman Swan: So there was a dose effect; the worse your sleep apnoea, the worse your cancer outcome.

David Gozal: That's correct. So we took a little different slant. What none of these studies looked at was quality of sleep, and it seemed to us that when you have sleep apnoea it's not just that your levels of oxygen go down and up but in fact you have to wake up to catch your breath, and you may do this many, many times during the night, and we call this fragmented sleep. We looked at the literature and looked at the incidence of cancer in populations who lived very close to very noisy environments, and there is a little bit of a suggestion that indeed if you live on a highway or next to an airport there are more cardiovascular disease and cancer. So it seems that it's not just the amount of sleep because patients with sleep apnoea sleep the same amount as normal people…

Norman Swan: Except they have these micro-awakenings.

David Gozal: Exactly, they have these micro-awakenings, they have their sleep fragmented throughout the night, that's why they are sleepy during the day. So we argued that can we look at the effect of fragmented sleep without all the other perturbations that occur in sleep apnoea and will we see a biological effect? So to do that you have to do the true mechanistic experimentation and cause and effect in mice, and that's where we started our experiment.

So what we set out to do was a very simple experiment. We had developed a way of measuring and inducing fragmentation of sleep in mice, and we took genetically identical mice, we injected them with the same amount of cancer cells. And in one group of mice they were fragmented, in other words they were as if they had to wake up every two minutes. They maintained their usual social setting, they ate the same way that they wanted to eat, they drank the same…

Norman Swan: They fell asleep at the wheel the next day.

David Gozal: Fell asleep at the wheel the same day, did exactly what they would have wanted to do, but the only difference was that when there was a standard time to go to sleep we would wake them up every two minutes, very gently, it's not stressful, we had validated all that. The other group was not disturbed. And lo and behold, as the tumours started growing, we identified that there was an accelerated tumour growth in the group that was fragmented during sleep.

Norman Swan: And you also tried to find out why.

David Gozal: Absolutely. We did many, many experiments. We really wanted to be sure. The second thing that we asked is; is it specific for this type of cancer? So we used another type of cancer, and lo and behold we found exactly the same. So we used a different type of cancer, a little bit more aggressive cancer, and we saw an inordinate acceleration of growth in mice that were interrupted during their sleep compared to those that were not. So that told us that this seemed to be at least applicable to all types of solid cancers. And then, as you indicated, the question was why. So we needed to…

Norman Swan: Just before you go there, did you increase the frequency of fragmented sleep so you got a dose effect?

David Gozal: No, we did not. Those are clearly things that might be very interesting once we establish the plausibility of the phenomenon because what we did was to mimic a relatively severe condition, and now the question is; is there a threshold, is there a time at which, even if you have a little bit of fragmented sleep, it's not going to make an effect? Those are all very important questions, but first we need to make sure that indeed you have an effect and that you can identify some degree of mechanisms before you now start identifying when those mechanisms are activated or not activated.

Norman Swan: So what was causing this problem with the tumour?

David Gozal: Well, we don't know what is causing the problem. We believe that there are some pathways that are involved, and so in order to look at that the first thing that we looked at was what happens to the immune system in these mice that are fragmented. Why did we look at the immune system? For two reasons. One, because the immune system is very important in controlling cancer. When we have a cancer, we have a recognition of cancer cells as foreign, and if we do and our immune system targets those as foreign substances they will fight it and they will try to destroy it and remove them. That's actually what happens in normal conditions before we ever develop cancer. Our body produces once in a while in the process of reproducing cells, one of them will be cancerous, and…

Norman Swan: Our body mops it up.

David Gozal: And the body's immune system mops it up and gets rid of it. There comes a time that it doesn't, and then there is obviously this innate immune system, this is one that could be very important, and the innate immune system involves a certain type of cells called macrophages.

Norman Swan: These are the chomping-up cells, the cells that chew up rubbish.

David Gozal: They mop up infection, they mop up everything that is foreign to the body.

Norman Swan: The Harvey Keitels of the immune system.

David Gozal: Exactly, I like that analogy. So these macrophages, the problem is that they are not all are born equal. There are what we call type 1 macrophages, these are the good ones, the ones that know how to become Harvey Keitels and remove all these tumours, and then there are other types, one that is called type 2 or type 2 like which actually promotes tumour, it's a suppressor of inflammation. They are very important in our body, they turn off the immune response when it's not needed, they…

Norman Swan: They calm everything down, but in this situation you don't particularly want it to be calmed down.

David Gozal: Exactly. And so these macrophages seem to concentrate and the tumour seems to induce these macrophages to become type 2, to become the low activity ones, the mellow macrophages. And when they become mellow they release substances that…what they do is to promote the formation of vasculature, of new vessels, of matrix, and allow for the tumours to grow even faster.

So we looked for those macrophages and we found that in fragmented interrupted mice there were a lot of those type 2 macrophages that were particularly in the periphery of the tumour, while in the non-fragmented mice we saw M1 macrophages in the core of the tumour. So this was very, very impressive as a finding, and we said, well, wait a second, is it possible that fragmented mice have produced a different kind of macrophage or induced a crosstalk between the tumour and the macrophages from the host to become mellow, to change the way they respond to the tumour, and in fact instead of fighting the tumour they are helping the tumour to grow.

So we set about checking whether this was the case, and we looked at a variety of markers in those peripheral macrophages that looked like M2, and indeed they had the markers of M2, and we found that they expressed one innate marker which is called toll-like receptor 4, TLR4. TLR4 is very important, and it's been involved in cancer biology…

Norman Swan: In fact there are new drugs that target this receptor.

David Gozal: Absolutely. And so it was surprising. Why is TLR4 so highly expressed in these mellow macrophages that are helping the tumour to grow? So now we needed to go to the background of our ability to change the genetics of mice and make them specifically according to design, so designed mice. So we started with a designed mouse that did not have TLR4. So their macrophages would not be able ever to produce TLR4. And not only did we find that the tumours shrank when we injected them into these genetically engineered mice, but that the differences between interrupted and non-interrupted sleep completely disappeared.

So we believe that what is happening is that interrupted sleep is changing our innate immune system, it's giving miscues to the innate immune system to become more pro-tumour, accommodating into a good neighbour policy, and therefore rather than fight the tumour it is willing to partner with the tumour by inducing these markers that then communicate between the tumour cells and the body and allow for the tumour to grow, and not only to grow. So the second thing that we found is that these tumours became much more aggressive. Now, what do we mean by aggressive? These tumours not only grew bigger but they started being able…and we did experiments to show that, that these tumours when you were under interrupted sleep conditions were able to cross the boundaries of their capsule and enter the other tissues, healthy tissues.

Norman Swan: So more likely to metastasise or spread, as they say.

David Gozal: At least locally. We don't know yet and we are going to be studying whether they can metastasise to remote sites, but at least locally they were able to invade muscle, to invade surfaces of other healthy tissues, even to eat the bone, even though in a non-interrupted mouse we never saw that. So I think that the conclusions from the study is that there is no doubt that sleep, integrity of sleep or quality of sleep seems to be a very important determinant of the biological fate of tumours. And the second conclusion that I think is also very important is that we have identified or at least confirmed that the TLR4 seems to be a good target for development of therapeutic strategies.

So I think that by helping cancer biologists and indicating that TLR4 is a viable target but also by identifying sleep as yet another factor that needs to be incorporated in the way that clinicians and patients think about their cancer, that healthy sleep is probably also a very good fighter against cancer and may help in having optimal outcomes.

Norman Swan: So, two questions; one is not everything that happens in a mouse happens in humans.

David Gozal: Absolutely. The only analogies that we can give is we know that because we have done those experiments in mice that if you interrupt sleep in a mouse they have sleepiness, they develop also sleepiness even though they sleep the same amount, and they have cognitive and learning deficits. That happens also in humans, exactly the same. We know that if we perturb sleep in the way we have done with these mice, that they develop some degree of cardiovascular complications. That's exactly what we found in humans. We know that if we perturb sleep in mice that they develop substantial metabolic disturbances. That's exactly what we find in humans. So I would like to say that if it walks like a duck, it quacks like a duck, let's believe that it's a duck.

Norman Swan: And the second question is did you try stopping fragmenting their sleep to see whether any of this was reversible?

David Gozal: No, we haven't, and this obviously is a very important facet.

Norman Swan: But you don't just study mice, you study real human beings and children with sleep apnoea, and you're looking for a much simpler way of assessing the severity or the problem without having to go into a sleep laboratory.

David Gozal: Yes. As a paediatrician we've been interested in sleep apnoea in children for quite some time.

Norman Swan: Why do children get sleep apnoea? Tonsils and adenoids is one reason, and presumably obesity is another, but are there any other reasons?

David Gozal: Well, you have said about 90% of the major factors. There are others. Of course children who have neuromuscular diseases or children that have specific craniofacial genetic syndromes, all these are obviously at a very high risk, premature infants also have poor growth of their mandible and so that is associated with a high risk of sleep apnoea. But the most important are really enlarged tonsils and adenoids, and obesity, and they affect 1% to 3% of all children. So it is a frequent disease, much more frequent than people would believe. And we have always indicated that even habitual snoring, which is a very frequent symptom in many children, it affects in fact about 10% of children across the globe, about a quarter of those children will have sleep apnoea.

Norman Swan: Meaning that they have pauses where they stop breathing.

David Gozal: They have pauses in which they stop breathing, their levels of oxygen may drop, and also they may wake up interruptedly, and so they will not have a very optimal quality of sleep and, as you know, children need more sleep than adults, indicating that sleep is a very important and vital function and one that we should never ignore.

So we know from studies that we have conducted and others have conducted over the last two decades that sleep apnoea in children leads to learning deficits, poor academic performance in school, hypertension, metabolic dysfunction, sometimes bedwetting, aggressive behaviours, inattentive behaviours, depression and so on, and leads to also increased healthcare costs. So there is good reason of why we need to diagnose it.

At this time, questionnaires or a history and a physical exam by a physician are not very good. It's almost like tossing a coin. And so a sleep study in the laboratory or at least in very specialised conditions at home, which is a costly endeavour, it is labour-intensive, it's inconvenient to families, to children, and sometimes there is no access to it. So that has prevented a much wider recognition and detection of the disease.

And so we figured that if you have all these perturbations, that there must be a signal somewhere, either in the blood or in the urine that we would be able to pick up. And so over the last few years we were able to identify that there is indeed a signature in the urine of children with sleep apnoea that I believe will help us.

Norman Swan: And what is it?

David Gozal: We find that there are a certain group of proteins that are altered in the urine, and that if we were to do a very simple 'pregnancy test', so a simple strip test or a laboratory test that will just look at the levels of those proteins, we would be able to identify accurately a very large proportion of children that at least have sleep apnoea. Of course if you are symptomatic and negative then you would need to be evaluated the way we do it today.

Norman Swan: So where do these proteins come from? The immune system or are the kidneys damaged or what?

David Gozal: It's a mix of oxidative stress markers that come into the urine, because when you have all these awakenings and low levels of oxygen there's increased oxidative stress. It's inflammatory markers that come as proteins that indicate that there has been increased inflammation process.

Norman Swan: And can you monitor progress? In other words, when the child is treated for sleep apnoea do these proteins go away?

David Gozal: That's a great question, yes, they do.

Norman Swan: How do you treat sleep apnoea in children?

David Gozal: So the first line of treatment at the moment for children with sleep apnoea is to take their tonsils and adenoids away. We know that this will lead to a substantial improvement in about 85% of the children, not everybody, but it doesn't lead to complete cure in a relatively large proportion; 40%, 50% do not get completely cured.

So our laboratory has also been very interested in developing nonsurgical cures or at least treatments for the milder cases, and in fact we have recently published our experience on a very large cohort of children that we have treated systematically as part of our clinical protocol where we showed that a topical treatment with nasal steroids, and a little pill that is used for asthma usually or for allergies, both together are actually quite effective in very mild sleep apnoea that probably could avoid going to surgery in the vast majority of cases.

Norman Swan: You squirt steroids up the nose, like as if you had hay fever.

David Gozal: That's right, and we give a little pill that is an anti-asthma medication, preventive medication called montelukast, and this combination seems to be very effective in reducing the need for surgery in groups of children that have very mild sleep apnoea. Of course if you have a more severe one we still advocate the surgical interventions in order to reduce the likelihood of complications from the disease.

Norman Swan: And you've done randomised trials to show it?

David Gozal: Not yet. We have done randomised controlled trials for single agents, not for the combination.

Norman Swan: David Gozal, who is Professor of Paediatrics at the University of Chicago.